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. 2019 Nov 13;9:16699. doi: 10.1038/s41598-019-53235-w

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Functional motor units innervating forelimb muscles were assessed by motor unit number estimation in vivo. (A) Electrophysiological setup to record compound muscle action potential (CMAP) and incremental single motor unit potentials (SMUPs) in the left ventromedial forearm (forelimb), which houses the wrist flexor muscles (flexor carpi radialis m., flexor digitorum profundus m., palmaris longus m., flexor digitorum superficialis m.). The red needle electrodes are stimulating electrodes, which straddle the brachial plexus. The active recording electrode (E1) is placed on the left ventromedial forearm and the reference recording electrode (E2) overlies the left wrist while a ground electrode is in contact with the tail. Anaesthesia is induced and maintained with isoflurane, and normal body temperature is preserved with a heating pad (see Methods section for more details). (B) Representative CMAP response from the ventromedial forearm region. Baseline-to-Peak (B-P) CMAP amplitude is determined by measuring between the baseline (I) and the negative peak (II) of the waveform, while Peak-to-Peak (P-P) CMAP amplitude is determined by measuring between the negative peak (II) and the positive peak (III). X-axis represents time (ms) and y-axis represents voltage (mV). Sensitivity: 200 mV, 20 mV per division; Duration: 10 ms, 1 ms per division. (C) Representative incremental acquisition of ten SMUP waveforms. SMUP amplitude is determined by measuring between negative peak (I) and positive peak (II). X-axis represents time (ms) and y-axis represents voltage (µV). Sensitivity: 2 mV, 200 µV per division; Duration: 10 ms, 1 ms per division. (E) Baseline values of B-P CMAP (51.3 ± 0.7), P-P CMAP (76.5 ± 0.7), SMUP (185.4 ± 3.6) and motor unit number estimation (MUNE; 415 ± 8) obtained from recordings in naïve rats. Data presented as mean ± SEM and n = 18 for each value. (D) Test-retest of values involved in MUNE calculation: P-P CMAP (), SMUP (), and MUNE values (●) obtained from the wrist flexors of naïve rats; n = 6 rats, with three tests per animal. Low test-retest variation is evident by mean coefficient of variation values (P-P CMAP: 4.5%; SMUP: 8.4%; MUNE: 9.4%).

Inline graphic — Functional motor units innervating forelimb muscles were assessed by motor unit number estimation in vivo. (A) Electrophysiological setup to record compound muscle action potential (CMAP) and incremental single motor unit potentials (SMUPs) in the left ventromedial forearm (forelimb), which houses the wrist flexor muscles (flexor carpi radialis m., flexor digitorum profundus m., palmaris longus m., flexor digitorum superficialis m.). The red needle electrodes are stimulating electrodes, which straddle the brachial plexus. The active recording electrode (E1) is placed on the left ventromedial forearm and the reference recording electrode (E2) overlies the left wrist while a ground electrode is in contact with the tail. Anaesthesia is induced and maintained with isoflurane, and normal body temperature is preserved with a heating pad (see Methods section for more details). (B) Representative CMAP response from the ventromedial forearm region. Baseline-to-Peak (B-P) CMAP amplitude is determined by measuring between the baseline (I) and the negative peak (II) of the waveform, while Peak-to-Peak (P-P) CMAP amplitude is determined by measuring between the negative peak (II) and the positive peak (III). X-axis represents time (ms) and y-axis represents voltage (mV). Sensitivity: 200 mV, 20 mV per division; Duration: 10 ms, 1 ms per division. (C) Representative incremental acquisition of ten SMUP waveforms. SMUP amplitude is determined by measuring between negative peak (I) and positive peak (II). X-axis represents time (ms) and y-axis represents voltage (µV). Sensitivity: 2 mV, 200 µV per division; Duration: 10 ms, 1 ms per division. (E) Baseline values of B-P CMAP (51.3 ± 0.7), P-P CMAP (76.5 ± 0.7), SMUP (185.4 ± 3.6) and motor unit number estimation (MUNE; 415 ± 8) obtained from recordings in naïve rats. Data presented as mean ± SEM and n = 18 for each value. (D) Test-retest of values involved in MUNE calculation: P-P CMAP (), SMUP (), and MUNE values (●) obtained from the wrist flexors of naïve rats; n = 6 rats, with three tests per animal. Low test-retest variation is evident by mean coefficient of variation values (P-P CMAP: 4.5%; SMUP: 8.4%; MUNE: 9.4%).